1. Field of the Invention
The present invention relates to a novel polyacetal resin composition, and more particularly to a polyacetal resin composition simultaneously having an excellent high-temperature stiffness and an excellent lubricity.
2. Related Art
Polyacetal resin is an engineering resin excellent in strength characteristics, fatigue resistance, self-lubricating property, etc., and is extensively in use in many fields such as automobiles, machines, electrical industry, electronic industry and the like. On the other hand, polyamide resin is an engineering resin excellent in impact resistance, frictional resistance, abrasion resistance, flexibility, etc., and is extensively in use in many fields such as automobiles, machines, electrical industry, electronic industry and the like, similarly to polyacetal resin.
In the recent years, higher properties have become required of these engineering resins, and today such requirements cannot be satisfied by a single resin. Thus, polymer alloys, such as a polymer alloy formed between polyacetal resin and polyolefin resin are observed with interest.
On the other hand, regarding polymer alloy made of polyacetal resin and polyamide resin, no method capable of controlling the morphology of such a polymer alloy is known, and therefore no polymer alloy simultaneously retaining a high stiffness at high temperatures and a good lubricity has yet to be found.
As examples of a blended mixture consisting of a polyacetal resin and a polyamide resin, a polyacetal resin composition prepared by adding 1-40 parts by weight of an inorganic powdery material to 100 parts by weight of a composition consisting of 5% by volume or more of a polyacetal resin and 95% by volume or less of a polyamide resin (Japanese Patent Application Kokai (Laid-Open) No. 63-34377) and a polyacetal resin composition prepared by dispersing a polyamide having a maximum particle diameter of 10 .mu.m and consisting of 90% by weight or more of a polyacetal resin and 0.01-10% by weight of a polyamide resin (4,6-nylon) into a polyacetal resin (Japanese Patent Publication No. 2-11625) are known. There is described in Japanese Patent Kokai No. 63-34377 that another resin having a melting temperature similar to that of polyoxymethylene may be mixed in producing a synthetic resin needle valve having high anticorrosion, employing polyoxymethylene in place of metal; as an example thereof, there is disclosed the above composition. Also, there is disclosed in Japanese Patent Unexamined Publication (KOKAI) No. 2-11625 the above composition employing a specific polyamide having a high melting point in order to prevent polyamide added to polyoxymethylene as a heat stabilizer from separating out in a molding machine screw or a metal mold. In those prior art references, there are no description nor suggestion as to the composition of a polyacetal resin and a polyamide resin having both high temperature stiffness and lubricity.
On the other hand, it is a well known technique to reinforce a polyacetal resin with a filler, such as glass fiber and the like, for the purpose of enhancing its high-temperature stiffness. However, the reinforcing effect brought about by this technique has been small, because polyacetal resin is poor in wetness at the interface with filler, such as glass fiber and the like, and therefore quite low in adhesive strength to glass fiber and the like. In addition, such a reinforcement using a filler has been disadvantageous in that it simultaneously deteriorates the lubricity to a large extent, which is an original property of polyacetal resin.